Rotator cuff tears are common, affecting 50% or more of the population over age 60. This condition in painful and often results in long-term shoulder disability even after surgical repair. Treatment typically begins with 6-12 weeks of physical therapy (PT). If PT fails to improve pain or strength, then the torn rotator cuff is often repaired surgically. Some evidence suggests that performing surgery earlier in the patient's course of treatment may result in a better outcome, but the decision to forego PT in favor of surgery is not easy since the relative effectiveness of PT and surgical repair is not known. Furthermore, it is also not known why PT is effective for some patients while other patients require surgical repair. Our long-term goal is to optimize the treatment of rotator cuff tears. The objective of this study is to quantify the effectiveness of PT and surgical repair in treating smal rotator cuff tears. Our central hypothesis is that improvements in clinical outcomes (pain, strength) after PT or surgery are significantly associated with shoulder motion. Specifically, we hypothesize that decreased pain is associated with decreased impingement, and that improved strength is associated with the extent to which glenohumeral joint (GHJ) and scapulothoracic motions are restored to normal. To better understand the treatment of rotator cuff tears, our approach will be to longitudinally measure shoulder strength, GHJ motion, scapulothoracic motion, and pain in rotator cuff patients prior to beginning PT, after 8 weeks of PT, and up to one year after surgery. Guided by findings from the previous grant period, our central hypothesis will be tested by pursuing the following specific aims: 1) compared to age-matched control subjects with normal shoulder function, determine the extent to which rotator cuff pathology affects shoulder motion and strength, 2) in patients with small rotator cuff tears, determine the extent to which physical therapy affects the relationship between pain, strength, and shoulder motion, and 3) in patients for whom PT is not successful, determine the extent to which surgical repair affects the relationship between pain, strength, and shoulder motion. The proposed research is innovative because it will use a state-of-the-art motion measurement technique (biplane x-ray analysis) to provide a highly accurate assessment of the effects of physical therapy and surgical repair on in-vivo GHJ and scapulothoracic motion. Understanding the complex relationships between dynamic shoulder motion, strength, and pain - and how these relationships are affected by operative and non-operative interventions - will provide the framework to explain current clinical outcomes and lead to improved clinical interventions. This contribution will be significant because it will advance our understanding of the treatment of rotator cuff tears and will ultimately lead to improved patient care.